The present invention relates to a hydraulic dual-circuit tandem master brake cylinder for vehicle brake systems having a closed brake circuit and an open brake circuit. The closed brake circuit has a brake piston and the open brake circuit has an auxiliary piston/control valve device actuated by a push rod and reinforced by auxiliary pressure.
In this known master brake cylinder, it is difficult to make the actuation of the control valve sufficiently sensitive. Furthermore, given the disposition of the master brake cylinder and the amplifier in a row, the volume of the two brake circuits substantially determines the pedal-travel characteristic. Such systems are widely distributed. However, disposing dual-circuit master brake cylinders, and in particular a tandem master brake cylinder, in a row with an amplifier produces a structure of great length. Furthermore, the status of ventilation of a brake circuit or a failure in the brake circuit as well has a direct effect on the brake pedal. Futhermore, in the event of an amplification failure great force must be exerted by the foot on the pedal in order to produce braking pressure, since the dimensions of the master cylinder pistons can be designed only for intact amplifiers.
If a travel-limiting spring or some other travel simulator inserted between the brake pedal and the control valve is used, the travel-limiting spring determines the pedal characteristic.
In that event, the above-discussed disadvantages are avoided in part. This is true particularly if the two master cylinders are disposed parallel to and beside one another, as is known from German Offenlegungsschrift No. 29 07 922, for instance. However, such a design differs very greatly from present-day conventional constructions, so that mass production would have to be preceded by a great expenditure for testing.